A) CORRECT. Although utilities pay less for low-quality coal, they must use more of it and also bear expenditures involved in ash disposal. Therefore a policy of always buying low-quality coal might not always lead to economic benefit if the costs are greater than the savings.
B) Incorrect. Even if the cost of disposing coal ash is negligible, utilities must buy more of low-quality coal to generate the same amount of electricity. Therefore the savings from buying low-quality coal (as compared to high-quality coal) may be mitigated through the increased usage of low quality coal. Therefore we cannot conclude reasonably that buying high-quality coal will be more expensive in this situation.
C) Incorrect. We are not given any details on the proportion of costs involved so cannot make this conclusion.
D) Incorrect. We are given no information about disposal costs, so we cannot compare.
E) Incorrect. The rate of decline of coal reserves are not based on the costs involved in disposing off ash generated through burning the coal. We cannot reasonably draw this conclusion.

A) is therefore the correct answer.